Comparing the Response Characteristics and Volumetric Water Balance in Three Unit Hydrograph Methods (A case study: Vanak Basin)

Unit Hydrograph is a method for flood hydrograph simulation resulting n response to a unit of excess rainfall on the basin. The theory for unit hydrograph is based on two systematic principles called superposition and proportionality. So far several methods of unit hydrograph has been developed which show different responses and functionalities under local conditions of the basin. In this study we used a continuous hydrologic simulation from HEC-HMS model to compare the performance of three unit SMA algorithm and linear reservoir were selected as loss and base-flow functions of the basin, respectively. The flood hydrograph and its specifications including peak discharge and runoff volume were derived using three ways of Snyder, Clark and SCS methods. To compare the performance of models the Nash - Sutcliffe Efficiency was considered as as the objective function. Parameterization and validation of the hydrological parameters were done by changing parameters manually and a applying a trial-error method. Results showed for all three methods the percent of differences between the simulated and observed volumes for runoff was quite very close to each other. While in term of peak flows, the Clarke unit hydrograph method showed the best agreement between the simulated and observed peak discharges.